Power dissipation in valves.

[GrimJosef]

Tungsten, or perhaps a tungsten/moly alloy e.g. the Eimac 304TL. Between the 125W filaments and the 300W anode dissipation they light the room up nicely https://www.vintage-radio.net/forum/...ad.php?t=40860. You light up too if you get at all involved with the HT supply .

Cheers,

GJ

[PJL]

Interesting question.

The voltage difference between the cathode and anode determines the electrons acquired kinetic energy dissipated in the anode. The current is the number of electrons reaching the anode.

[David Simpson]

Martin, have a look back to Diabolical Artificer's(aka Andy) thread which started on 8th of this month. That's the most recent of several in-depth discussions on thermionic valves in recent times.
Using a transistor for comparison purposes might get a bit confusing for some folk considering their streams of electrons, be it Ic, Ib or Ie. They're governed more by doping Silicon or Germanium with Arsenic, Antimony or Indium, or whatever, and the resultant complicated valency bonding. The kinetic energy of electrons leaving a heated thoriated tungsten Cathode & belting a few mm or more through a vacuum to a +ve Anode is a totally different scenario, electronics-wise.
Back to basics is my advice. Read up on DeForrest, and the later post WW1 development of Bright Emitter & Dull Emitter valves. Then into the late 20's/early 30's change from Filaments to separately heated cathodes. Then the change from PX power triodes to KT b/tetrodes, and so on. Back then much research was put into anodic heat dissipation.

Regards, David

[Radio Wrangler]

Choice of metals for grids was dominated by the issue of secondary emission. They chose materials with high work functions to reduce emission from everything other than cathodes.

Gas absorption is by getters. Getters were rings of metal with a channell shaped cross section. In the bottom of the trough they put something like barium and then plated nickel over it. After the valve had been heated and pumped to outgas it, the envelope was sealed off and an induction heater was placed near the getter from the outside of the tube. The getter was flashed to high temperature, evaporating first the nickel and depositing it on the inside of the bulb, then came the reactive metal deposited on top of the nickel on the bulb. The reactive stuff was now exposed to the environment inside the envelope and could catch stray gas molecules.

The over-plating on the getter rings allowed them to be handled in air during assembly of the valve.

If you kept the anode/cathode voltage fixed and moved the anode further from the cathode, the field would be less intense, electrons would be get a lower rate of acceleration, but over the longer distance. The effects cancel,and the arrival speed is the same at the anode. So the kinetic energy is Va electron-volts for each electron. Then take into account the charge on an electron and hence the number flowing per amp, and you get the power arriving as Va * Ia as the electron charge and the number flowing simplify.

Va * Ia is the power dissipated and also the electrical power expected to be dissipated.

It all fits together like a jigsaw. Something would be badly wrong if it didn't!

David